Cold-starting of internal combustion engines, particularly small engines in chain saws, snow blowers and the like, has been and remains a problem in the art. Devices such as chain saws which are frequently employed under adversed starting conditions typically embody a manual priming system, as illustrated in U.S. Pat. No. 4,271,093 (June 2, 1981), in which a resilient cap or bulb is mounted on or adjacent to the engine carburetor and may be manually activated by an operator for drawing fuel into the carburetor and purging air therefrom. Excessive activation of the cap or bulb when the engine is cold typically results in ejection of fuel into the surrounding environment. Moreover, activation of the priming system when the engine is warm, or where the engine fails to start on the first attempt, can so flood the engine carburetor that the engine will not start at all.
Parent U.S. application Ser. No. 118,629, filed Nov. 9, 1987 and assigned to the assignee hereof, discloses a fuel delivery system for purging air from the reservoir of a diaphragm carburetor on an internal combustion engine and for supplying priming fuel to the carburetor air intake. A pump is responsive to electrical signals from a priming control circuit to the draw fuel through the carburetor reservoir and to feed fuel under pressure to a nozzle positioned at the carburetor air intake. The electronic control circuitry is responsive to an operator for initiating a priming operation and includes a temperature sensor coupled to the engine for a controlling a first timer which determines time duration of the priming operation, and thus the quantity of engine priming fuel, as a function of engine temperature. A second timer is responsive to operator initiation of a priming operation for preventing regeneration of the priming control signal to the pump, and thereby preventing attempted repriming in the event of failure of the engine to start.
Although the automatic priming systems so disclosed in the parent application overcome deficiencies in the prior art noted in the preceding paragraph, a problem remains in that such automatic systems are fairly expensive to implement on small, relatively inexpensive engine-driven devices. There thus remains a need in the art for a purging and priming system of a described character which is directly responsive to quantity of fuel actually injected during a priming operation, which indicates to an engine operator that a purging and priming operation has been completed, which will retain such indication for an extended time duration so as to advise an operator that the priming operation should not be repeated, and which is less expensive to the manufacture and implement than are devices of the described character heretofore proposed. It is a general object of the present invention to provide a system which addresses such need.
More specifically, it is an object of the present invention to provide a purging and priming system of the described character which will facilitate one-pull starting of an engine over an extended temperature range, which is so constructed as to discourage misuse by an inexperienced operator, including particularly overpriming of the engine, which is powered by replaceable batteries, which is reliable over an extended operating lifetime, and which requires minimum adaptation to particular engine designs and requirements.